1. Field of the Invention
The present invention relates to an electron multiplier and a photomultiplier tube, and more particularly relates to an electron multiplier and a photomultiplier tube provided with a focusing electrode plate.
2. Description of Related Art
In a photomultiplier tube disclosed in Japanese Patent Unexamined Patent Application (Kokai) No. 6-314550, a photocathode is formed on the internal surface of a faceplate. A plate-shaped focusing electrode is provided in confrontation with the photocathode. The focusing electrode plate includes a focusing portion having a plurality of openings and a frame portion surrounding the focusing portion.
A block-shaped dynode unit is located below the focusing electrode plate. The dynode unit is constructed from a plurality of plate-shaped dynodes laminated one on another. Each dynode plate has a plurality of electron multiplication through-holes or channels, each for multiplying electrons. The plurality of electron multiplication through-holes are formed in each dynode plate in correspondence with the plurality of openings at the focusing electrode.
An anode unit and an inverting dynode plate are successively disposed below the dynode unit. The inverting dynode plate is for inverting the orbits of electrons multiplied by and emitted from the dynode unit. The anode unit is provided for receiving the electrons supplied from the inverting dynode plate. The anode unit has a plurality of anodes which are located in correspondence with the respective through-holes or channels in the dynode unit.